Despite persistent reports of concern within the Reagan administration about the civil war in El Salvador, the State Department yesterday said it considers the U.S-supported, civilian-military government to be "stronger today than it was at the beginning of the year."

Department spokesman Alan Romberg, commenting on the challenge to the Salvadoran government from leftist guerrillas, said: "Politically, it has held together despite intense pressures from the extreme right and extreme left and has emerged more unified and stronger than ever."

Romberg's comments came amid reports that the administration believes the war has reached a stalemate and that the government headed by civilian President Jose Napoleon Duarte could be defeated unless the United States takes new steps to bolster it.

In recent interviews, Secretary of State Alexander M. Haig Jr. has said that a stalemate exists and that the Duarte government needs more U.S. aid.

However, in the latest interview, published yesterday by The New York Times, Haig stressed that no decisions have been made about the size and nature of new aid or possible measures to combat the flow of outside military assistance to the guerrillas.

Romberg said the military situation "is stalemated in the sense that neither side can win in the short term, but it is our view that the Salvadoran military capability continues to improve."

However, Haig, in an interview last week with Newsweek magazine, gave a gloomier assessment: "Stalemate could ultimately be fatal because Salvador is experiencing grievous economic difficulties . . . combined with the continual fighting and bloodshed."

Since last summer, administration officials dealing with Central America have expressed disappointment at the Duarte government's inability to end the guerrilla threat.

Some reports, including one published this week by the Times, have said Haig has been pressing the Defense Department to consider possible military action within El Salvador and against Cuba and Nicaragua, which have been accused of aiding the guerrillas.

However, the Pentagon is understood to have resisted any significant broadening of the U.S. involvement on grounds that it might provoke a Soviet retaliation in another part of the world and would probably trigger intense opposition from the American public and Congress.

A new sign of congressional restiveness at the administration's policy came Thursday, when the House inter-American affairs subcommittee voted, 9 to 0, for a resolution urging President Reagan to "press for unconditional discussions" among the warring Salvadoran factions to help guarantee open elections in March.

The bipartisan move was viewed as a call for the administration to ease the Cold War attitudes it has projected into the Salvadoran situation and encourage more flexibility in dealing with the left, which supports the guerrillas.

However, Romberg insisted yesterday that the resolution was in accord with the administration's policy of urging the guerrillas to stop fighting and cooperate in the electoral process.

He said that, while the administration might have worded it differently, it welcomed the resolution as being in agreement with Reagan's goals.

Sen. Christopher J. Dodd (D-Conn.) yesterday called for Haig to appear before the Senate Foreign Relations Committee to explain his interview statements and administration policy toward El Salvador, Cuba and Nicaragua.

Dodd contended that Haig, in testimony March 19, assured him that the committee would be consulted before the administration undertakes any major new initiatives in the Salvadoran situation.

In the Times interview, Haig indicated that his major concern is finding ways to cut off the supply of arms to the guerrillas. He said he was not ruling out actions outside El Salvador.

But he refused to specify whether the administration is looking at such options as a naval blockade of Nicaragua or a show of force involving air and naval exercises around Cuba.

Although there have been hints that these ideas are under study, Defense Secretary Caspar W. Weinberger and the Joint Chiefs of Staff are understood to be resisting them.